the first person or thing of a certain name; something from which another person or thing takes its name ...1880 rare
from proto- (first, first-formed) + Greek ὄνοµα, ὄνυµα (name), after synonym
FIRST DOCUMENTED USE
1880 - see EXAMPLE below
"...And here they saw the wrecked canal-boat, the Evening Star, ignominiously quenched in the twilight, with its heavenly protonym palpitating in the vapor above it..."
From: Scribner's Monthly
An Illustrated Magazine for the People.
Conducted by J.G. Holland
Vol XIX, March, 1880, No. 5
The Tile Club Afloat